Gamma-Ray Bursts in the Swift and Fermi era
Wu Xuefeng, Purple Mountain Observatory, Chinese Academy of Sciences

Gamma-ray bursts are one of the most puzzling mysteries in modern astronomy. The discovery of their afterglows in X-ray, optical and radio bands in 1997 helped astronomers to understand the underlying hydrodynamics and radiative processes. I will review the standard relativistic fireball-shock model for gamma-ray bursts, as well as the central engine models for the long and short bursts. Since lunched in 2004, the Swift satellite has made a lot of new discoveries such as X-ray flares in the early afterglow phase and the recent "naked-eye" burst. I will talk about the post-standard models for these new phenomena. The Fermi gamma-ray large area space telescope has detected more than 10 gamma-ray bursts with GeV photon emission since it was launched in June 2008. These GeV emission are key clue to identifying different radiative processes of prompt gamma-ray emission, which was unclear before. With GeV photons and their time lag relative to MeV photons in two recent bursts, GRB 080916C and GRB 090510, we constrained the lower limits ( >~1000 ) on the bulk Lorentz factor (speed) of these two gamma-ray bursts, and the lower limit on the quantum-gravity mass if Lorentz invariance is violated according to some loop quantum-gravity models. Finally, I will discuss the possibility of Ordovician extinction caused by an ancient gamma-ray burst.

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